n = int(input())
a = [int(input()) for i in range(n)]
ans = 0
a.sort(reverse=True)
for i in range(n):
    if a[i]:
        ans += 1
        now = a[i]
        a[i] = 0
        for j in range(i+1,n):
            if now > a[j]+1:
                now = a[j]
                a[j] = 0
print(ans)